Re: Add pg_stat_autovacuum_priority

> 0001:
>
> -                                      AutoVacuumScores *scores);
> +                                      AutoVacuumPriority *priority);
>
> IMHO we need to minimize these kinds of extraneous changes in this patch
> set.  AutoVacuumScores still seems accurate enough, even when the struct
> contains some extra bool members.
>
> - * A table whose autovacuum_enabled option is false is
> - * automatically skipped (unless we have to vacuum it due to freeze_max_age).
> - * Thus autovacuum can be disabled for specific tables. Also, when the cumulative
> - * stats system does not have data about a table, it will be skipped.
> + * A table whose autovacuum_enabled option is false is automatically skipped
> + * by autovacuum (unless we have to vacuum it due to freeze_max_age),
> + * but scores are still computed.  Also, when the cumulative stats system does
> + * not have data about a table, threshold-based scores will be zero.
>
> I don't think we need to update this comment.
>
> - * One exception to the previous paragraph is for tables nearing wraparound,
> - * i.e., those that have surpassed the effective failsafe ages.  In that case,
> - * the relfrozen/relminmxid-based score is scaled aggressively so that the
> - * table has a decent chance of sorting to the front of the list.
> + * Furthermore, for tables nearing wraparound, i.e., those that have surpassed
> + * the effective failsafe ages, the relfrozen/relminmxid-based score is scaled
> + * aggressively so that the table has a decent chance of sorting to the front
> + * of the list.
>
> Or this one.

Fixed both.

> + * Priority scores are always computed.  dovacuum and doanalyze are only set when
> + * autovacuum is active and enabled for the relation.
>
> I think we should more explicitly state that while scores->needs_vacuum and
> friends are always set regardless of whether autovacuum is enabled, the
> return parameters dovacuum, etc., are not.

I made this more explicit by saying " All fields in AutoVacuumScores
are always computed
regardless of autovacuum settings...." I think that is clear enough.

> Or perhaps we should return
> whether autovacuum is enabled in the struct and consolidate the return
> parameters and the struct members.  WDYT?

dovacuum, doanalyze will be unused by callers like the sql function, and putting
them in the struct could make this cleaner, but I don't think it's
worth it to blur
the purpose of the struct. I rather keep it just for score computation purposes.

> 0002:
>
> Seems fine.

I found a bug in my v4 that I fixed.

+        if (elevel > 0 && vac_ins_base_thresh >= 0)

is wrong. It should be:

if (elevel > 0)
{
      if (vac_ins_base_thresh >= 0)


> 0004:
>
> +    FROM pg_stat_get_autovacuum_priority() S
> +         JOIN pg_class C ON C.oid = S.relid
> +         LEFT JOIN pg_namespace N ON N.oid = C.relnamespace;
>
> What do you think about ordering by score so this view automatically shows
> the tables most in need of vacuuming/analyzing first?

I thought about that initially, but we don't really have an example where the
data is ordered in a stats view ( or any other catalog view ), and I prefer not
to impose that on the user automatically.

See v5.

--
Sami